1. Field of the Invention
The present invention relates to a recording apparatus that records images, such as characters, figures, and patterns, on a recording medium.
2. Related Background Art
There has been known conventionally the so-called serial recording apparatus that records on the surface of a recording medium by enabling the carriage that mounts a recording head thereon to travel in the direction orthogonal to the carrying direction of the recording medium. With the serial recording apparatus thus arranged, images are recorded on a recording medium by repeating the recording operations to carry the recording medium and to move the carriage alternately. In general, the carriage travels along the carriage shaft, and a motor is used as the driving power therefor. The driving power of the motor is transmitted to the carriage through a timing belt which is tensioned around the pulley of the motor and partly fixed to the carriage.
In recent years, there have been more demands to the higher image formation, and the materialization of high image quality as well. To meet such demands, a structure is adopted so that images are recorded by use of plural lines of pixel arrays each formed by plural pixels. Then, for example, a color recording apparatus or the like has been proposed with a carriage which is provided with the plural recording heads each using yellow, magenta, cyan, and black, respectively, in a state where these heads are arranged side by side in the traveling direction of the carriage, thus performing color printing by overlaying each of the colors as required.
Here, when the motor is driven as the driving source of carriage movement as described above, the traveling speed of the carriage is subjected to the changes of its speed due to the run-out (eccentricity) of the driving pulley, for example. The changes of carriage speed that may take place in such a manner tend to bring about the unevenness of recording images eventually. For the color recording apparatus or the like which performs the color recording by overlaying each of the colors with the carriage having the four-color heads arranged on it side by side in the traveling direction of the carriage, such recording unevenness is allowed to appear as the deviation of each color in a recording image, and results in the degradation of image quality ultimately.
Of the serial recording apparatuses described above, the ink jet recording apparatus which performs the image recording by discharging ink droplets from the recording heads, in particular, finds it necessary to make the distance between each of the plural recording heads substantially equal to the moving amount of the driving pulley per rotation or integral times such moving amount in order to reduce the degradation of image quality due to the changes of carriage speed. A structure of the kind has been disclosed in the specification of Japanese Patent Application Laid-Open No. 03-246059 and the specification of Japanese Patent Application Laid-Open No. 05-155092, for example. Also, in the specification of Japanese Patent Application Laid-Open No. 06-91896 and the specification of Japanese Patent Application Laid-Open No. 09-248922, it has been disclosed that the timing of ink discharges is made changeable for each of the recording heads in order to correct the changes of carriage speed due to the pulley run-out.
The problems described above are caused by the changes of the carriage speed. Here, the cycle of the speed changes is relatively large, such as almost equivalent to one cycle of the pulley. However, the cycle of the speed changes is relatively small as the component of acceleration. For the conventional ink jet recording apparatus, the unevenness of recorded images and the color deviation may take place due to the positional deviation of the recording heads caused by such changes of the carriage speed at the time of discharging ink. For example, therefore, it may be possible to solve the problems by effectuating the discharge timing appropriately by use of an encoder or the like provided within the traveling range of the carriage.
However, among the factors that may cause the speed changes of the carriage, there are, besides the one described above, those having a relatively small cycle, but relatively large component of acceleration, which are caused by the vibrations due to the gap between the tooth of the timing belt, the torque ripple of the motor, or due to the vibration frequency inherent in the vibrating system of the driving systems as a whole.
The image unevenness and color deviation that may be caused by those factors described above are smaller than those caused by the eccentricity of the pulley or the like. However, the aforesaid vibrations or the like caused by the minute vibrations due to the "play" between the carriage having the recording heads mounted thereon, and the carriage shaft, which may also bring about the image unevenness and color deviation, cannot be prevented by the provision of the structure whereby to make the timing of ink discharges appropriate by use of the encoder or the like.